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<strong class="selflink"> Expressions</strong><div class="t-navbar-menu"><div>
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<tr class="t-nv-h2"><td colspan="5"> General </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="value_category.html" title="cpp/language/value category"> value categories</a> (lvalue, rvalue, xvalue)</td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="lambda.html" title="cpp/language/lambda">lambda-expression</a><span class="t-mark-rev t-since-cxx11">(C++11)</span>
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<tr class="t-nv-h2"><td colspan="5"> Literals </td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="nullptr.html" title="cpp/language/nullptr">null pointer literal</a><span class="t-mark-rev t-since-cxx11">(C++11)</span>
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<tr class="t-nv"><td colspan="5"> <a href="user_literal.html" title="cpp/language/user literal">user-defined literal</a><span class="t-mark-rev t-since-cxx11">(C++11)</span>
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<tr class="t-nv-h2"><td colspan="5"> Operators </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_assignment.html" title="cpp/language/operator assignment"> Assignment operators</a>: 
<code>a=b</code>, <code>a+=b</code>, <code>a-=b</code>, <code>a*=b</code>, <code>a/=b</code>, <code>a%=b</code>, <code>a&amp;=b</code>, <code>a|=b</code>, <code>a^=b</code>, <code>a&lt;&lt;=b</code>, <code>a&gt;&gt;=</code>
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</td></tr>
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<code>+a</code>, <code>-a</code>, <code>a+b</code>, <code>a-b</code>, <code>a*b</code>, <code>a/b</code>, <code>a%b</code>, <code>~a</code>, <code>a&amp;b</code>, <code>a|b</code>, <code>a^b</code>, <code>a&lt;&lt;b</code>, <code>a&gt;&gt;b</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_logical.html" title="cpp/language/operator logical"> Logical operators</a>: <code>a||b</code>}, <code>a&amp;&amp;b</code>, <code>!a</code>
</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_comparison.html" title="cpp/language/operator comparison"> Comparison operators</a>: <code>a==b</code>, <code>a!=b</code>, <code>a&lt;b</code>, <code>a&gt;b</code>, <code>a&lt;=b</code>, <code>a&gt;=b</code>
</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_member_access.html" title="cpp/language/operator member access"> Member access operators</a>: <code>a[b]</code>, <code>*a</code>, <code>&amp;a</code>, <code>a-&gt;b</code>, <code>a.b</code>, <code>a-&gt;*b</code>, <code>a.*b</code>
</td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_other.html" title="cpp/language/operator other"> Other operators</a>: <code>a(...)</code>, <code>a,b</code>, <code>(T)a</code>, <code>a?b:c</code> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="operator_alternative.html" title="cpp/language/operator alternative">Alternative representations of operators</a>
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<p>An expression is a sequence of <i>operators</i> and their <i>operands</i>, that specifies a computation.
</p>
<p>Expression evaluation may produce a result (e.g., evaluation of <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span></span></span> produces the result <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">4</span></span></span>) and may generate side-effects (e.g. evaluation of <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../io/c/fprintf.html"><span class="kw1524">std::<span class="me2">printf</span></span></a><span class="br0">(</span><span class="st0">"%d"</span>,<span class="nu0">4</span><span class="br0">)</span></span></span> prints the character <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">'4'</span></span></span> on the standard output).
</p>
<table id="toc" class="toc"><tr><td>
<div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="expressions.html%23General"><span class="tocnumber">1</span> <span class="toctext">General</span></a></li>
<li class="toclevel-1 tocsection-2">
<a href="expressions.html%23Operators"><span class="tocnumber">2</span> <span class="toctext">Operators</span></a>
<ul>
<li class="toclevel-2 tocsection-3"><a href="expressions.html%23Conversions"><span class="tocnumber">2.1</span> <span class="toctext">Conversions</span></a></li>
<li class="toclevel-2 tocsection-4"><a href="expressions.html%23Memory_allocation"><span class="tocnumber">2.2</span> <span class="toctext">Memory allocation</span></a></li>
<li class="toclevel-2 tocsection-5"><a href="expressions.html%23Other"><span class="tocnumber">2.3</span> <span class="toctext">Other</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-6">
<a href="expressions.html%23Primary_expressions"><span class="tocnumber">3</span> <span class="toctext">Primary expressions</span></a>
<ul>
<li class="toclevel-2 tocsection-7"><a href="expressions.html%23Literals"><span class="tocnumber">3.1</span> <span class="toctext">Literals</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-8"><a href="expressions.html%23Unevaluated_expressions"><span class="tocnumber">4</span> <span class="toctext">Unevaluated expressions</span></a></li>
<li class="toclevel-1 tocsection-9"><a href="expressions.html%23Discarded-value_expressions"><span class="tocnumber">5</span> <span class="toctext">Discarded-value expressions</span></a></li>
</ul>
</td></tr></table>
<h4>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: General">edit</a>]</span> <span class="mw-headline" id="General">General</span>
</h4>
<ul>
<li> <a href="value_category.html" title="cpp/language/value category">value categories</a> (lvalue, rvalue, glvalue, prvalue, xvalue) classify expressions by their values
</li>
<li> <a href="eval_order.html" title="cpp/language/eval order">order of evaluation</a> of arguments and subexpressions specify the order in which intermediate results are obtained
</li>
</ul>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Operators">edit</a>]</span> <span class="mw-headline" id="Operators">Operators</span>
</h3>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="7"> Common operators
</th>
</tr>
<tr style="text-align:center">
<td> <a href="operator_assignment.html" title="cpp/language/operator assignment"> assignment</a>
</td>
<td> <a href="operator_incdec.html" title="cpp/language/operator incdec"> increment<br>decrement</a>
</td>
<td> <a href="operator_arithmetic.html" title="cpp/language/operator arithmetic"> arithmetic</a>
</td>
<td> <a href="operator_logical.html" title="cpp/language/operator logical"> logical</a>
</td>
<td> <a href="operator_comparison.html" title="cpp/language/operator comparison"> comparison</a>
</td>
<td> <a href="operator_member_access.html" title="cpp/language/operator member access"> member<br>access</a>
</td>
<td> <a href="operator_other.html" title="cpp/language/operator other"> other</a>
</td>
</tr>
<tr style="text-align:center">
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">=</span> b<br>
a <span class="sy2">+</span><span class="sy1">=</span> b<br>
a <span class="sy2">-</span><span class="sy1">=</span> b<br>
a <span class="sy2">*</span><span class="sy1">=</span> b<br>
a <span class="sy2">/</span><span class="sy1">=</span> b<br>
a <span class="sy2">%</span><span class="sy1">=</span> b<br>
a <span class="sy3">&amp;</span><span class="sy1">=</span> b<br>
a <span class="sy3">|</span><span class="sy1">=</span> b<br>
a <span class="sy3">^</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;&lt;=</span> b<br>
a <span class="sy1">&gt;&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a<br>
<span class="sy2">--</span>a<br>
a<span class="sy2">++</span><br>
a<span class="sy2">--</span></span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span>a<br>
<span class="sy2">-</span>a<br>
a <span class="sy2">+</span> b<br>
a <span class="sy2">-</span> b<br>
a <span class="sy2">*</span> b<br>
a <span class="sy2">/</span> b<br>
a <span class="sy2">%</span> b<br>
~a<br>
a <span class="sy3">&amp;</span> b<br>
a <span class="sy3">|</span> b<br>
a <span class="sy3">^</span> b<br>
a <span class="sy1">&lt;&lt;</span> b<br>
a <span class="sy1">&gt;&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span>a<br>
a <span class="sy3">&amp;&amp;</span> b<br>
a <span class="sy3">||</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b<br>
a <span class="sy3">!</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;</span> b<br>
a <span class="sy1">&gt;</span> b<br>
a <span class="sy1">&lt;=</span> b<br>
a <span class="sy1">&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">[</span>b<span class="br0">]</span><br>
<span class="sy2">*</span>a<br>
<span class="sy3">&amp;</span>a<br>
a<span class="sy2">-</span><span class="sy1">&gt;</span>b<br>
a.<span class="me1">b</span><br>
a<span class="sy2">-</span><span class="sy1">&gt;</span><span class="sy2">*</span>b<br>
a.<span class="sy2">*</span>b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp">a<span class="br0">(</span>...<span class="br0">)</span><br>
a, b<br>
<span class="br0">(</span>type<span class="br0">)</span> a<br>
<span class="sy4">?</span> <span class="sy4">:</span></span></span>
</p>
</td>
</tr>
<tr>
<th colspan="7"> Special operators
</th>
</tr>
<tr>
<td colspan="7">
<p><a href="static_cast.html" title="cpp/language/static cast"><tt>static_cast</tt></a> converts one type to another compatible type <br>
<a href="dynamic_cast.html" title="cpp/language/dynamic cast"><tt>dynamic_cast</tt></a> converts virtual base class to derived class<br>
<a href="const_cast.html" title="cpp/language/const cast"><tt>const_cast</tt></a> converts type to compatible type with different <a href="cv.html" title="cpp/language/cv">cv</a> qualifiers<br>
<a href="reinterpret_cast.html" title="cpp/language/reinterpret cast"><tt>reinterpret_cast</tt></a> converts type to incompatible type<br>
<a href="../memory/new/operator_new.html" title="cpp/memory/new/operator new"><tt>new</tt></a> allocates memory<br>
<a href="../memory/new/operator_delete.html" title="cpp/memory/new/operator delete"><tt>delete</tt></a> deallocates memory<br>
<a href="sizeof.html" title="cpp/language/sizeof"><tt>sizeof</tt></a> queries the size of a type<br>
<a href="sizeof....html" title="cpp/language/sizeof..."><tt>sizeof...</tt></a> queries the size of a <a href="parameter_pack.html" title="cpp/language/parameter pack">parameter pack</a> <span class="t-mark-rev t-since-cxx11">(since C++11)</span><br>
<a href="typeid.html" title="cpp/language/typeid"><tt>typeid</tt></a> queries the type information of a type<br>
<a href="noexcept.html" title="cpp/language/noexcept"><tt>noexcept</tt></a> checks if an expression can throw an exception <span class="t-mark-rev t-since-cxx11">(since C++11)</span><br>
<a href="alignof.html" title="cpp/language/alignof"><tt>alignof</tt></a> queries alignment requirements of a type <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</p>
</td>
</tr>
</table>
<ul>
<li> <a href="operator_precedence.html" title="cpp/language/operator precedence"> operator precedence</a> defines the order in which operators are bound to their arguments
</li>
<li> <a href="operator_alternative.html" title="cpp/language/operator alternative"> alternative representations</a> are alternative spellings for some operators 
</li>
<li> <a href="operators.html" title="cpp/language/operators">operator overloading</a> makes it possible to specify the behavior of the operators with user-defined classes.
</li>
</ul>
<h4>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Conversions">edit</a>]</span> <span class="mw-headline" id="Conversions">Conversions</span>
</h4>
<ul>
<li> <a href="implicit_cast.html" title="cpp/language/implicit cast"> standard conversions</a> implicit conversions from one type to another
</li>
<li> <a href="const_cast.html" title="cpp/language/const cast"> <code>const_cast</code> conversion</a>
</li>
<li> <a href="static_cast.html" title="cpp/language/static cast"> <code>static_cast</code> conversion</a>
</li>
<li> <a href="dynamic_cast.html" title="cpp/language/dynamic cast"> <code>dynamic_cast</code> conversion</a>
</li>
<li> <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast"> <code>reinterpret_cast</code> conversion</a>
</li>
<li> <a href="explicit_cast.html" title="cpp/language/explicit cast"> explicit cast </a> conversion using C-style cast notation and functional notation
</li>
<li> <a href="cast_operator.html" title="cpp/language/cast operator">user-defined conversion</a> makes it possible to specify conversion from user-defined classes
</li>
</ul>
<h4>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Memory allocation">edit</a>]</span> <span class="mw-headline" id="Memory_allocation">Memory allocation</span>
</h4>
<ul>
<li> <a href="new.html" title="cpp/language/new"> new expression</a> allocates memory dynamically
</li>
<li> <a href="delete.html" title="cpp/language/delete"> delete expression</a> deallocates memory dynamically
</li>
</ul>
<h4>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Other">edit</a>]</span> <span class="mw-headline" id="Other">Other</span>
</h4>
<ul>
<li> <a href="constant_expression.html" title="cpp/language/constant expression"> constant expressions </a> can be evaluated at compile time and used in compile-time context (template arguments, array sizes, etc)
</li>
<li> <a href="sizeof.html" title="cpp/language/sizeof"> <code>sizeof</code> </a>
</li>
<li> <a href="alignof.html" title="cpp/language/alignof"> <code>alignof</code> </a>
</li>
<li> <a href="typeid.html" title="cpp/language/typeid"> <code>typeid</code> </a>
</li>
<li> <a href="throw.html" title="cpp/language/throw"> throw-expression </a>
</li>
</ul>
<p><br>
</p>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Primary expressions">edit</a>]</span> <span class="mw-headline" id="Primary_expressions">Primary expressions</span>
</h3>
<p>The operands of any operator may be other expressions or primary expressions (e.g. in <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy2">*</span><span class="nu0">3</span></span></span>, the operands of operator+ are the subexpression <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">2</span><span class="sy2">*</span><span class="nu0">3</span></span></span> and the primary expression <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span>).
</p>
<p>Primary expressions are any of the following:
</p>
<div class="t-li1">
<span class="t-li">1)</span> Literals (e.g. <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">2</span></span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"Hello, world"</span></span></span>)</div>
<div class="t-li1">
<span class="t-li">2)</span> Suitably declared <a href="name.html" title="cpp/language/identifiers">unqualified identifiers</a> (e.g. <span class="t-c"><span class="mw-geshi cpp source-cpp">n</span></span> or <span class="t-c"><span class="mw-geshi cpp source-cpp">cout</span></span>)</div>
<div class="t-li1">
<span class="t-li">3)</span> Suitably declared <a href="name.html" title="cpp/language/identifiers">qualified identifiers</a> (e.g. <span class="t-lc"><a href="../string/basic_string/npos.html" title="cpp/string/basic string/npos">std::string::npos</a></span>)</div>
<div class="t-li1">
<span class="t-li">4)</span> <a href="lambda.html" title="cpp/language/lambda">Lambda-expressions</a>
</div>
<p>Any expression in parentheses is also classified as a primary expression: this guarantees that the parentheses have higher precedence than any operator.
</p>
<h4>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Literals">edit</a>]</span> <span class="mw-headline" id="Literals">Literals</span>
</h4>
<p>Literals are the tokens of a C++ program that represent constant values embedded in the source code.
</p>
<ul>
<li> <a href="integer_literal.html" title="cpp/language/integer literal">integer literals</a> are decimal, octal, hexadecimal or binary numbers of integer type.
</li>
<li> <a href="character_literal.html" title="cpp/language/character literal">character literals</a> are individual characters of type <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char16_t</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">char32_t</span></span></span>, or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">wchar_t</span></span></span>
</li>
<li> <a href="floating_literal.html" title="cpp/language/floating literal">floating-point literals</a> are values of type <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>, <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span>, or <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span>
</li>
<li> <a href="string_literal.html" title="cpp/language/string literal">string literals</a> are sequences of characters, which may be narrow, multibyte, or wide
</li>
<li> <a href="bool_literal.html" title="cpp/language/bool literal">boolean literals</a> are values of type <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span>, that is <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> and <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span>
</li>
<li> <a href="nullptr.html" title="cpp/language/nullptr">nullptr</a> is the pointer literal which specifies a null pointer value <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</li>
<li> <a href="user_literal.html" title="cpp/language/user literal">user-defined literals</a> are constant values of user-specified type <span class="t-mark-rev t-since-cxx11">(since C++11)</span>
</li>
</ul>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Unevaluated expressions">edit</a>]</span> <span class="mw-headline" id="Unevaluated_expressions">Unevaluated expressions</span>
</h3>
<p>The operands of the four operators <a href="typeid.html" title="cpp/language/typeid"><tt>typeid</tt></a>, <a href="sizeof.html" title="cpp/language/sizeof"><tt>sizeof</tt></a>, <a href="noexcept.html" title="cpp/language/noexcept"><tt>noexcept</tt></a>, and <a href="decltype.html" title="cpp/language/decltype"><tt>decltype</tt></a> are expressions that are not evaluated, since these operators only query the compile-time properties of their operands. Thus, <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n <span class="sy1">=</span> sizeof<span class="br0">(</span><a href="../io/basic_ostream.html"><span class="kw1439">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="nu0">42</span><span class="br0">)</span><span class="sy4">;</span></span></span> does not perform console output.
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx14">
<td>
<p>The unevaluated operands are considered to be <i>full expressions</i> even though they are syntactically operands in a larger expression (for example, this means that <span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span>T<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> requires an accessible <code>T::~T</code>)
</p>
</td>
<td><span class="t-mark-rev t-since-cxx14">(since C++14)</span></td>
</tr>
</table>
<h3>
<span class="editsection">[<a href="http%3A//en.cppreference.com/mwiki/index.php" title="Edit section: Discarded-value expressions">edit</a>]</span> <span class="mw-headline" id="Discarded-value_expressions">Discarded-value expressions</span>
</h3>
<p>A <i>discarded-value expression</i> is an expression that is used for its side-effects only. The value calculated from such expression is discarded. Such expressions include the full expression of any <a href="statements.html%23Expression_statements" title="cpp/language/statements">expression statement</a>, the left-hand argument of the comma operator, or the argument of a cast-expression that casts to the type <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span>.
</p>
<p>Array-to-pointer and function-to-pointer conversions are never applied to the value calculated by a discarded-value expression. The lvalue-to-rvalue conversion (in other words, a memory read), however, is applied, but only if the expression is a <a href="cv.html" title="cpp/language/cv">volatile-qualified</a> glvalue and has one of the following forms (possibly parenthesized)
</p>
<ul>
<li> id-expression
</li>
<li> array subscript expression
</li>
<li> class member access expression
</li>
<li> indirection
</li>
<li> pointer-to-member operation 
</li>
<li> conditional expression where both the second and the third operands are one of these expressions,
</li>
<li> comma expression where the right operand is one of these expressions.
</li>
</ul>
<p>In addition, if the expression is of class type, it needs a volatile copy-constructor to initialize the resulting rvalue temporary.
</p>
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